Electrical signaling system



EQB. IREL AND ET AL ELECTRICAL SIGNALING SYSTEM April 14,1942.

Filed Sept. 16, 1959 3 Sheets-Sheet 1 IN VENTORS.

EPIC BERTR] IRELAND ER! WYN JONES ATTORNEY.

p 1942- E. B. IRELAND EFAL 2,279,568

ELECTRICAL SIGNALING SYSTEM Filed Sept, 16, 1939 5 'Sheets-Sheef 2INVENTORS ERIC 'BERTRAM IRELAND ERIC WYN JONES ATTORNEY.

g; E -q$ F --------R i E a; I I a April 14, 1 E. B.|RELAND EI'AL- ELECTRICALSIGNALING SYSTEM Filed Sept. 16,. 1939 3 Sheets-Sheet 3 INVENTORSERIC BERTRAM IRELAND RIC WY/V JONES 1 ATTORNEY.

Patented Apr. 14, 1942 UNITED STATES PATENT orrics f ELECTRICALSIGNALING SYSTEM Eric Bertram Ireland, Liverpool, and Eric Wyn Jones,Nottingham, England, assignors to Associated Telephone & TelegraphCompany, Chicago, 111., a corporation of Delaware Application September16, 1939, Serial No. 295,176 In Great Britain September 1'7, 1938 11Claims.

The present invention relates to electrical signaling systems and ismore particularly con, cerned with systems for transmitting fire alarmsignals to a central station from a plurality, of boxes located atdifferent points all of which will usually be accessible to the public.

The invention has particular application to fire alarm systems of theclosed circuit type in.

which a plurality of boxes are series connected in a loop circuit overwhich a current normally flows. With this arrangement a calling streetbox is arranged to transmit a series of impulses indicative of its codenumber to the central station where an indication of the number is givenand to improve the reliability of the system it is usually arranged thatthe box is earthed during sending and the loop is interrupted accordingto th appropriate code on both sidesof the earth connection.

The general object of the invention is to provide improved arrangementswhereby calls from short-circuited fire alarm boxes shall be satis-.

factorily handled with the minimum of interference with thenormalworking of the system.

According to one feature of the inventionin a fire alarm system of theclosed circuit type arranged so that when a box is pulled interruptionsin a loop circuit and also intermittent connections to earth areproduced, the code from a short-circuited box is satisfactorily receivedby arrangingthat when earth is intermittently applied to the circuitwithout the loop being in-.

terrupted, th connections are automatically al-.

tered so that the code represented by theintermittent earth connectionsproduces operation of the code responding equipment. p

According to another feature. of the invention, in a fire alarm systemof the.closed cir.- cuit type arranged so that when a box is pulledinterruptions in the loop circuit and also inter-' mittent connectionsto earth are. produced, as

soon as a box is pulled earth is connected to the loop and serves toinitiate a test whereby conditions are established such that if the loopis not, satisfactorily opened when the earth connection is removed, thecircuits of the code re sponding equipment are altered so that the coderepresented by the intermittent earth'connections produces operation ofthe responding equipment.

A further feature of the invention in a' fire alarm system of the closedcircuit type arranged so that when a box is pulled interruptions in theloop circuit and also intermittent connections to earth are produced, assoon as a box is pulled" earth is connectedto the loop and serves to initiate a test whereby conditions are established such that if the loopis not satisfactorily opened when the earth connection is removed, adevice responsive to the intermittent earthconnections is enabled toproduce corresponding interrup-rl Considering the circuit operation ofFigs. 1.

and 2, the general operation, in response toa normal fire call with allboxes in order will firstb dealt with. Assuming that .fire alarm box FA,Fig.1, is calling, the code wheel .begins .to rotate in a clockwisedirection, as shown, driving the off-normal cam in. a counter-clockwisedirection. These cams are arranged to operate the oif-normal contacts NIand N2 a short interval before the first operation of .the impulsecontacts IMF! and IMPZ, thereby .to provide an initial test period.During this period earth via.

rectifier MBA is therefore connected over contact N! to both conductorsof the first alarm loop. The high resistance earth test relay Ethereupon voperates and at armature e'l operates.

relay ER. Relay ER looks over its other winding to positive overarmatures erl, efl,'gr3 and do! and also at armature er2 short circuitsrelay E so as to provide a holding earth for th box succession coils Blor B2 and B3 under short-. circuited box conditions via the winding ofthe low resistance relay EX. Relay EX now operates and thereuponenergises relay EB, Fig. 2, which brings up relay EC and this relay'inturn operates relay ED at armature ccl. Relay EC also at armature ec2reverses the-polarity of the earth test circuit by connectingearth overrelay ET to the opposite pole of theloop battery BA. Relays E and EX arethereby disconnected, so that relay EX releases at about the same timeas relay ED is operated; Since earth is con-; nected to the loop overthe rectifier MBA at the calling box, relay ETwill be unable to operateunder this condition sincefthe rectifier To improve the op eratingconditions for relay-ET in case a faulty will not be conductive.

liammeter MA and may be adjusted-by the variable resistance VR. Theinitiation of a telephone call from a street box causesa resistance tobe inserted in the loop which reduces the: loop current to say 30milli-amps whereupon relay T releases and operates relay TA. as will .be

described subsequently, the remaining series equipment still being heldby this current; Relays RA and RE, the register PR and gong GG have allapproximately the same operating and releasingvalues andwill'operatewith a. current of th''orderof' 25 milli-amps and release with a currentof 11' milli-amps and under normal conditions" they will respondsatisfactorily to code impulsesL Under conditions where a box is'shuntedby a leak resistance as sometimes occurs, the" loop current will notdrop-to zero each time the box impulse springs open and conditionsmayarise where the relays. and puncher will receive sufiicient currentduring, the break periods to prevent their efiicient response. Tosafeguard the system from unreliable operation from this cause anadditional supervisory relay RS. is provided which will only release ifthe loop current fans to less than say milli-amps. If this relayremainsoperated when the first break is delivered from the box,short-ci'rcuited box working using earth return is immediately broughtinto operationso that the complete code transmitted is correctlyreceived. On the other hand if this relay releases, ordinary loopworking will be retained since under this condition the loop currentflow during break periods will clearly be so small as not to interferewith the:

proper operation of relay RA and the puncher and gong. Although relay RBis shown on. the drawing it is not concerned with the operationsinvolved in"carrying out the present invention and only performs auseful function. under earthe'd line break conditions.

' Continuing the description of normal operation from the point whenrelay EC operated during the initial test period of the calling box,relay EX will be released" as pointed out previously and relays EB andEU will release in turn. Relay EB thereuponcompletes an operatingcircuit for the slow-to-operate relay EF while the release of relay ECreconnects relays E and EX on to the loop. However since relay E' isstill short-circuited owing to the locking of relay ER, relay EX onlywill immediately operate and during the slow'rele'ase period of relay EDwhich commences to fall away on the release of relay EC, relay EWS willbe operated. Relay EWS locks up at armature e'wsl over its secondwinding and at armature ewsZ- opens the circuit of the slow-tooperaterelay EF before it has had time to oper- It, however, the operationsdescribed are initiated by a fault earth on the line rather than byvthepulling of a' box, relay ET will operate whenthe battery polarity on theline is reversed. Relay ET thereupon at armature etl, removes theshort-circuit from across relay ETR and so causes it to energise andlock up at armature etrl in series with relay EC. The latter relay thusremains held when relays EX and EB release so that no circuit isre-completed for relay EX and relay EWS cannot be operated overarmatures escl and edl as in the normal case. Consequently relay EFoperates shortly after the release of relay EB and at armature eJ2lights the earth fault alarm lamp EAL, at armature efl releases relaysETR and EC and at armatures ef3 removes the short circuit from relay Eso that ontherelease of relay EC relay E is again introduced into theearth test circuit. Relay E reoperates and ensures the maintenance ofrelays ER and'EF so that the earth alarm persists so long as the faultremains.

Continuing the description of a bona-fide call,

no further operation ensues until the fire alarm box transmits the firstbreak impulse of the train or trains constituting the box code and relayEX will then release and also the loop circuit relays T, RA andRS; Therelease. of relay RS indicates that no short-circuit exists on the boxso that no circuit is completed to the short-circuited box working relaySC and the call is received at the central station over the loop in thenormal manner. Relay P responds to impulses delivered from relay RA atarmature ml and repeats them tothe indicator circuit 10 while thereceived code is punched" on the tape by the register PR and sounded onthe. gong GG. Relay RS in responding to'the code impulses operates relayGR over armatures rs! and pl and this relay holds during pulsing due toits slug. When it operates, it releases relays ER and EWS bydisconnecting the holding. earth thereto at armature m3 and the earthcircuitrelays EX, E and ET are disconnected at armature gr2.

It will be understood that the armature of the fire alarm boxis madeslow-to-release in order that the box will hold in when relay EC ismomentarily operated during the earth discrimination test and removesthe holding earth for the callingbox earth succession coil.

- changes over the loop circuit to earth return working, the two sidesof the loop being connected in parallel over armature set and resistanceYA. Hence since the box impulse springs are broken at this moment relayRA, the

gong. GG and the register PR will release; relays T and. RS alsoreleases but these relays are not. concerned in the present operation.Suc

tain relay G which completes an, energising circuit for theslow-to-operate delay relay DA., It will be understood that althoughthis relay previously received impulses during the coding-in it wouldnot operate. During reception of the call relay GR was operated and dueto its slug remained energised and therefore released relays ER and EWSas pointed out above. On the operation of relay DA after a period of theorder of six seconds, relay SC is released and in turn opens the circuitof relay SCA which was operated when relay SC originally operated. Thefunction of relay SCA is to prevent relay DA operating relay EW and sobringing about full line break earth working on the fire alarm loopwhich differs from short-circuited box earth working in a manner to bedescribed. Relay SC on releasing restores the circuit to loop working,whereupon the line relays operate and release relay P which in turndisconnects relay DA. Due to its slug, relay SCA holds during this timeand prevents earth being extended over armatures dal, seal and gl tooperate relay EW. When the maintenance officer at the fire stationsubsequently operates the short-circuit call release key KSCR, relay SDwill be released at key contacts KSCRI to extinguish the short-circuitedbox call indication lamp SBL.

The short-circuited box earth working as described above which isemployed. whena call is received from a short-circuited box differsslightly from full earth working, this difference being mainly intendedto give improved possibilities of succession working if a good boxshould call when a box shunted by a fairly high resistance is alreadycoding-in. Under full earth working conditions, which are brought intoeffect in the relay DA. If a call is subsequently received either relaySA or relay SB (not shown) is operated in addition depending on whetherthe call is originated on the A or B leg. If the call is originated onthe A leg, relay SA is operated to disconnect the B leg at armature saland similarly for relay SB. By this means a second call originatedsimultaneously with the first and on the opposite leg is prevented fromsending in its code and so spoiling the code already being received fromthe first box. If, however, one leg were disconnected forshort-circuited box working as in the full earth working condition, itmight not be possible for a second good box calling on the same leg asthe first to hold the line relays operated in series with the resistanceacross the faulty box already coding and thus restores the loop workingcondition for succession working. It will be understood that if the linerelays failed to remain operated 7 due to the high value of theresistance across the faulty first box, the second good box would fallout but would maintain a continuous earth via its rectifier on to theline and would thus tend to interfere with the response of the linerelays to the earth pulses being transmitted from the faulty box alreadycoding. With the short-circuited box working shown however, both legs ofthe loop are kept intact and succession working between a second goodbox calling and an already running box having a fairly high resistanceshunt thereon can readily be effected, since when the second box callswith the first box already running, the earth extended from the-secondbox will immediately hold'the line relays operated round the other sideof the loop and so bring in loop working is the mannerto be nowdescribed.

When a call is being received from a short-.

circuited box andanother call is originated at a good box in the loop,the seco nd box on running f on its test tooth will extend'c'ontinuousearth via its rectifier on to the loop for such a time as will hold theline relays long enough to allow relay GR to release, this relaynormally receiving a pulse over armatures pl andrsl each time relay RSrestores due to the pulsing from thefirst box. Relay GR thereuponoperates relay SE over armatures yr! and s05 and this-relay at armaturese2 releases relay SC to allow ordinary loop line conditions to berestored; At armature se3 any possibility of short-circuiting the highresistance relay E in the earth test circuit is prevented so rent toflow through the loop succession coils'to hold them in whichcase thefirst break delivered by the second box will release the short-circuitedbox. When the shorted box falls out, the second good box carries oncoding-in; During this time relay GR will be again operated and releasesreand when the rectifier earth connection at the.

lay SE which again prepares a locking circuit for relay 80. After codingfrom the second box has been fully received the releasefof relay GRcauses earth to be reapplied to the earth circuit relays E and EX andthe'short-circuited box will again bring up relay SC in the usual mannerand will recommence to send in its'code.

. Considering nowthe case of a telephone call from a short-circuitedbox, the normal momentary increase of resistance in the loop circuitwill be clearly ineffective owing to the short-circuit on the box, butat the same time earth over the box rectifier is momentarily connectedto the line. It should be explained that in the case of a telephone callfrom a short-circuited fire alarm box the connection of the rectifierearth to the line would be effected manually by the fire or policeofficer initiating the call while in' the case" of a call from anambulance telephone box situated in the same loop as the fire alarmboxes this would be automatically effected, fo-r instance in the mannerdescribed in British specification No.

471,759. The momentary connection of the recti-.

fier earth to the line causes relay SC to hamperated in the manneralready described and this relay in turn operates reIays'SD and TA todisplay short-circuited box and telephone calls on the indicator panelby lighting the lamps SBL and TCL respectively. The operation of relaySC initiates short-circuited box working conditions box is removed, theline relays will release and bring up relay P which in turn operatesrelay G which completes a circuitto the delay relay DA. Relay DA onoperating after its slow period operates relay EW over its left-handwinding to bring about thechangeover to earth working so as to providefeeding current to the telephone instru-,

ment, not shown, at the calling box. Relay SD also at armature sci-3disconnects one winding of" the repeating coil RPC, which connects overleads l2 and I3 with the station telephone circuit, so

that when the telephone key KIS is operated,- speech may take placeunder this condition Clear downis subsequently effected by operating theshort-circuited box release key KSCR, whereupon at contacts KSCRlj relayISD is released and at contacts KSCRZ relayEW is released; Relay TA isreleased atv contacts KIfs hon theopera;

circuit is completed for the slow relay. DA and since relay EWS is notreleased by the operation of relay. GR afterthe predetermined periodrelay DA operates, and atjarmaturedal lightsthe socalled box earth lampBEL. Relay Du also at armature dal' releases relay EWS and this relaythereupon extinguishes the lamp BEL and disconnects the circuit to relayDA so that thecycle,

of operations repeatsitself .andcauses the lamp to flash; In. actual.practice it. might be more convenient to prevent. the earth test circuitfrom being continually broken down, and set up again as in', the circuitshown. byfarranging that relays DA and. EWS, on operating together bringup a relaywhich. locks and maintains either. a continousor intermittentcircuit for. thelamp BEL.

'Ifhe armature 002 in. the circuit of. relay DA'is to preventthisrelaybeing] brought in when during succession workingone or moreboxes fall out while another box is coding in." During this time itwill. be appreciated. thata rectifier earth. is. maintained on theloopandiit may-be maintained long enough to allow relay. DA to operate ifthecircuit to this relay is. not. broken. by relay CO. which. is operatedwhenv a. full code. has been received, at the central station.

Referring now. to Eig, 3'thi simply shows the essential equipmentrequired for handling shortcircuitedbox calls on straightiorwardsectorbox, i. 6 non-succession workingsystems. On anormal call from agood box, relaysfRA, RBand'T release in accordance, with the operationof the impulsing. springs. and the punch register. PR and gong GG areoperated in theusual. manner. Re-

lays BA and RBloperate slow relay RA whereby U the. earth testrelay E isdisconnected at armature p112, and does not produce any effect on theauxiliary equipment.

If the calling, box is shortecircuited however relay E operates by.wayoi the earth at the box. when. a call is initiated and atarmatureelcompletes a circuit for relay ER which in turn pulls up relay. Jwhich, locks, over. it lower winding. Relay J, at armature 9' 2completes a circuit for thetime delay relay EAwhich is utilised to bringin. an, earth alarm indication, after a period of the order of twelveseconds as will be. described subsequently. Relay. ER at. armature e12:operates, relay M of the countingrelays and this relay in turn prepares.a circuit for relay N which at this, stage is short-circuited by. thepositive potential extended from. armature ef3. It is assumed. thatthree-digitbox codes are to be catered for and on the transmission'ofthe hundreds digit, relay E responds to the impulses but relay ER dueto. its slug holds. operated during this time. It will be appreciatedthat due. to the short-circuit on the box relays RA, RB and T are unableto release so. that relayPA is not operated. During the interdigitalpause the impulsing springs.

atthe box. remain openso that. relay E releases, and duringthistimerelay ER 'willin turn release and remove the short-circuit from relay 7N. which operatesv in series with relay M which holds energised in thiscircuit. On the trans mission of the tens .digit relay E pulses andagain er tes, ela R wh h e sgrel a P a d. this relay in turn prepares acircuit for relay Q which at this time is short circuited, In thefin.ter-digitalpause following the tens digit, relay Q operates in series.with relay P. which remains held and after the reception of the unitsdigit relaysR and S will be operated in a similar'ma'hner. The operationof all'the relays MS indi j 'tes at on r c. ll. om a s r rwi ed.

box is in factbeing received, and relay Sat armature sl prepares acircuit for the short-circ uited box working relay SX.

11; Will beunderstood that each street box m l n i de n, ke a tetal f. re. ra smi sions of its box, number andhence when the first.v

make impulse of the hundreds digit is transmitted 0n the second round,relay E is again oper:

ated and brings up relay ER oncemore sothat. relay S2; is operated andlocks up over its lower winding On the first break impulse, relay' Ereleasesand now operates relay EP sincea circuit is completed for itover armatures el and sx5 and this relay thereupon breaks the loopcireuit at armature epl and thus repeats the pulse on to the line relaysand punchregister.

Relay PA now operates butin this case, the circuit,

for relay E is maintained over armature Relay RA also at armature paldisconnects any 'further operating circuit for relay S X though thisoperation serves no'useful function inthe present circumstances. Whenthe code wheel reaches the second make of the hundreds dig"? earth isre-applied totheline and relay Ejre operates since although relay EP isoperated at this time to disconnect the loop on the B leglthe earth willfeed round the A leg. Relay E on dp erating releases relay El? whichre-makes the loop circuit thereby re-energising the gong,

register and the line relays.

The second two codes transmitted from the box are thus translated fromearth pulses into loop pulses by relay EP and are correctly ceived onthepunch register and gong, the first code transmitted being lost inorder to diserim inate between a genuine call and momentary earthleakageson the line.

At the-conclusion of the code sending, relay E restores and maintainsrelay EP operated thereby breaking the loop circuit. Since. no furtherpulses are received on the punch register, after a further short delayperiod provided mechanically thereon, this restores to normal andmomentarily closes a pair of contacts pr tdoperate relay RR, which atarmatures TH and rr2releases the'relays SX, MS and J; Relay S on re:

leasing releases relay EP the loop circuit is thus re-made in readinessforfurther callsf Relay SX' when it operated initially energized relaySCB which remains locked over its lower wind mg and thus maintains theshort-circuited box call lamp SBL lighted until the cancel key KSCR isoperated by the station attendant.

In the case of an earth fault on the line, relay.

E remains steadily operated and brings up relays ER and J in turn. RelayJ completes, a

circuit for the delay relay EA and since relay PA is not now. operatedif the fault persists for twelve seconds or more relay EA operates andoperates relay EF. Relay EF locks up to the lamp EFL at armature ef2. ortwo momentary earth leakages n the line earth fault key EFK and lightsthe earth fault In the case of one which may be followed by continuousearth, a

number of the impulse train counting relays 5' MS may be operated andlocked, but these relays-will be released at armature ef3 when relay EFis operated.

" Itwill be understood that this latter method earth working on a linebreak. 'We claim: 1. In a fire alarm system, a call point and a centralstation, two conductors connecting said call point to said centralstation, said conductors normally connected together at said call point,

means at said call point for repeatedly interrupting the connectionbetween said conductors during the sending of a code to said centralstation, means for grounding said conductors at the call point wheneverthey are connected to- 5 gether during the sending of a code, saidgroundbeing disconnected from both conductors whenever said conductors aredisconnected from one I another during the sending of a code, a sourceof current at said central station normally connected between said twoconductors to cause cur-" rent to flow over said conductors in serieswhen they are connected together at said call point, means at saidcentral station responsive to interruptions of the current flow oversaid conductors in series, means operated at times to disconnect one ofsaid conductors from said source at said central station and to connectit to the other conductor, said last means also ef- Iective at saidtimes to ground said source thereby to cause current to flow from saidsource over said two conductors in parallel whenever said conductors aregrounded at said call point, said third means then responsive to theinterruptions of current flow over said two conductors in parallelwhenever the ground is disconnected from said conductors at said callpoint.

2. In a fire alarm system, a call point and a central station, twoconductors connecting said call point to said central station, saidconductors normally connected together at said call point, means at saidcall point for repeatedly interrupting the connection between saidconductors during the sending of a code to said central station, meansfor grounding said con- 5 ductors at the call point whenever they areconnected together during the sending of a code, said ground beingdisconnected from both conductors whenever said conductors aredisconnected from one another during the sending of a code, a source ofcurrent at said central station normally connected between said twoconductors to cause current to flow over said conductors in series whenthey are connected together at said call point, means at said centralstation responsive to interruptions of the current flow over saidconductors in series, other means at the central station operatedresponsive to the first disconnection of ground from said conductors atsaid call point during the sending of a code, 7

means operated ccnjointly by said last means and said third means todisconnect one of said conductors from said source at said centralstation and to connect it to the other of said conductors if said thirdmeans does not operate 7 responsive to the first disconnection of saidconductors from one another during the sending of a code, said lastmeans also efiective, upon operation, to ground said source thereby tocause current to flow from said source over said two conductors inparallel whenever said conductors are grounded at said call point, saidthird means then responsive to the interruptions of current flow oversaid two conductors in parallel whenever the ground is disconnected fromsaid conductors at said call point.

.3. In a fire alarm system, a call point and a central station connectedtogether by two conductors, a device at the central station forresponding to electrical impulses transmitted from said call pointduring the sending of an alarm therefrom, said responding devicenormally connected in a circuit including said two conductors in seriesand operated responsive to impulses transmitted over said two conductorsin series during the sending of an alarm from said call point, and meansoperated whenever said call point is short-circuited during the sendingof an alarm to change the connections of said responding device to saidconductors to render it responsive to impulses transmitted over said twoconductors in parallel.

4. In a fire alarm system as claimed in claim 3, wherein the sending ofan alarm from said call point is initiated by grounding said conductorsat the call point, means at the centralstation operative responsive to aground on said conductors to determine whether said ground is due to theinitiation of an alarm or to a fault.

5. In a fire alarm system as claimed in claim 3, wherein the sending ofan alarm from said call point is initiated by connecting ground througha rectifier to both of said conductors at said call point, means at saidcentral station for determining Whether a ground on said conductors isdue to the initiation of an alarm or to a fault, said means including asource of direct current at said central station connected across saidconductors, a test device for each of said conductors, and means forgrounding each of said conductors at said central station through itsrespective test device, both of said test devices being operated if theground on said line is due'to a fault, said rectifier preventing one ofsaid test devices from operating if the ground on said line is due tothe initiation of an alarm.

-6. In a central fire alarm station, two conductors incoming from a callbox circuit, a responding device normally connected in a circuitincluding said two conductors in series and responsive to electricalimpulses transmitted over said two conductors in series, and meansoperated at times for changing the connections of said device to saidtwo conductors, said means effective to ground said device thereby torender it responsive to electrical impulses transmitted over said twoconductors in parallel at said times.

7. In a fire alarm system, a call point connected to a central stationby a metallic loop circuit, means at said call point normally operatedto repeatedly interrupt said loop circuit during the sending of an alarmfrom said call point, thereby to transmit impulses over the two sides ofsaid circuit in series, a responding device normally connected in seriesin said loop circuit and operated by said impulses, means at said callpoint effective during the sending of an alarm therefrom if said callpoint is short-circuited to transmit impulses over the two sides .ofsaid responding device to said circuit to cause 1 it t0, respond to saidimpulses transmitted over the two sides of said circuit in parallel. n

8. .In a fire, alarm system, a call, point connected to a centralstation by, ametallic 100p circuit, a source of current in saidloopcircuit, a:

ground connection to said A loop circuit at the can point, means. at thecall :point for repeatedly interrupting saidloop circuitduring thesending of an alarm from saidcall point, said means effective also todisconnect ws id roundir ma least one side of saidloop circuit each timesaid loop circuit is interrupted, an jungrounded re- .Spondingdevice atsaid central.stationgconnected in series in said loop circuit andnormally opermated over the. .metallic, looni ir i x lusiv y 1 res onive t ea h in e ruption of said l op rcui c y saidfirst me nsha eroundedre pond n device at said cen ral station conne ted. to; Said can si eith llcopccircuitand op ra ed re po .A csivet c c rstd sco nec on of. vr ndfrcom said one side by said fir st means upon initiation of thesending of an alarm from said call point, and

means controlled conjointly by said two respondin g devi ces if said.first device fails to operate cQncurrently with said operation of saidsecond deviceto ground said first .device,, thereby to cause saidfirstdevice to respond to the repeated disconnections of saidgroundifrom said one side of said loop cir cuit by said first means 7 9.In a fire alarm system, av call. point'connected to a central stationJoya metallic loop circuit a source of current insaid loop circuit, aground connection to saidloop circuitat the call I point means at thecall point for repeatedly interruptingi said loop Circuit during the.sending of, an alarm. from said ,calldpoint, said means ef- ,f e ctivealsoto disconnecttsaid groundcfrom. at least one side of said loopcircuit. each time said loop circuit is interrupted, an, ungrounde'drespending device at said central station connected inseries in saidloop circuit andcnormallyioperated, over the metallic loopcircuit;,exclusively responsive to each interruption; of said loop;circuitby said firstameans agr'ounded responding device at saidcentral station, connected to.said

one side of the loop ,circuitHand-c at times operated responsive to eachdisconnectioncof ground from said one sideby said firstmeans, and meanscontrolled by said last responding device at said t me to i r fie saie99p u ta ac tra t pn. u on P3152 5 Q aid a device, therapy to insure theoperation of said s n nd n devii hu. 11;;

.01 1 0% re a a mls t tmb a a-99in? 91. eq e t a ce tr ta wmbra att lii. i99 circuit, a source of current in s aid loop circuit, a ound co n in. to s d .l9ena ait t. the ca oint me n a t e an. 129 t f r, r pea edlinterrupting said lO p circuit d ng the sending l t a a arm; om: aid..=.a l m i t. Sa d mean e t v a s t d sc nn t said. ree twee least oneside of said loop circuit eachfiime' said loop circuit is n e n nte r luncr wded-1esponding device at said central station connected in seriesin said loop circuit and normally operat eve e m t l 1 012, r uit v eluire T$FQY c a h iQPflEWfiPQQZ 99 Z$?iI- w t y i r m ns a ounded e eee n0.118 e 9 the 1 2 cir u a sier re eq 16 9.9 iv to ea d ec i n.- ..r9s1.. bm;a o e. d ub a d fi tlm an urin the-S nd n .Q a arm I r m vi a q.call p nt .i sai c 1 90 1 i o t ei wit d me ns n led: oun d .rc ie n inc dev ce, i9, Wh h r S i O era io o e d: und i 'e e nde v q s o ea 'nledb t ssa s s;o .v n alarm. f om aid ll mi aby; ae a t. on a 92. em tsandnmeaas c tr ed; y sa ro nd d r sp nd n :sieri t s d a t; m an det minh t a q er t qn 9 5 di r q p n i yi' ai oc asi n d y he send n er ealarm fr m. s id. ce p int to terruntsa 19 ci i ama d c ntra statien .pon; as' e n of sai gr und kl s o dina deri s her ei eratesa q lmgrw d de ond n v e e p te the che rtei qu tat a d c l-p i V. 1,- A fl e znc remc s c aimedz azclai l0 whe cmr aid fir tm ansison ated d rin h eendinp alarm tqn epeated tra smit, a r qetermine toda andwhem n saiddc e m .im n inc ude a .co nt rel yphainon rt d f ite cc danc wi h v he fir ttrnsmission'of said code when an alarm is sent-from said call point whilesaid call pointis shortfcircuited, thereby to distinguish:Operationibisaid grounded responding device. due to. the'lsending of analarm from operation: ofisaid' grounded device due to a fault in theloop circuit.

amcijsaaaamaams.

ERIC WYN JoNEs.

